Weight and Light

The weight force is the force of gravity, mass times g (the acceleration by gravity- 9.81 m/s^2).

The opposite of something being heavy/having a lot of weight is being light.

Light travels at the speed of light (c= 3*10^8 m/s) in a vacuum. The index of refraction (n) is calculated by dividing the speed of light in a vacuum by the speed of light through a substance (like air or glass), or by dividing the wavelength of light in a vacuum by the wavelength of light in the substance. n is then used in Snell's law (n1sin(theta1)=n2sin(theta2)) to determine the angle light will bend when it refracts between substances.